Electrodynamic and electroacoustical apparatus



2 P 1942-v h. E. BOWLEY 2,295,527

ELECTRODYNAMIC AND ELECTROACOUSTICAL APPARATUS Filed Oct. 17, 1940 INVENTOR Patented Sept. 15, 1942 CAL APPARAT Raymond E. Bowley, San Anselmo, CaliL, by decree oiidistribution to Eve Mary Bowley Application October 1'7, 1940, Serial No. 361,593

2 Claims.

This application for U. S. Letters Patent is a modification and continuation in part of Patent No. 2,189,161 issued February 6, 1940, and copending application for Letters Patent in U. S. Serial No. 317,266 filed February 5, 1940, allowed May 29, 1941, not issued. This invention is also a modification of the apparatus described and claimed in Reissue Patent No. 20,395 issued June reproducing diaphragms each carrying a signal current coil ina magnetic air-gap, wherein one diaphragm is larger than the other and is of the direct acting type, and the smaller diaphragm is of the relatively solid small type in acoustic relationship with a tubular resonant air column or with the air column of a horn passing through the inner pole portion of the electro-dynamic actuating unit and also through the center of the direct acting type diaphragm, whereby both diaphragms will project sound waves in substantially the same general direction and in substantially concentric relationship, the sound waves passing through an oriilced baflle in acoustical coupled relationship with the direct acting type diaphragm. v g

The present invention also relates to an improved electro-acoustic system comprising electro-dynamic means for actuating the diaphragm or diaphragms thereof, at least one direct actin type diaphragm, oriiiced baflie means acoustically coupled with the diaphragm, and a dividing-compensating-coupling circuit network in cooperative combination, employing acoustical conduction resonance action to the rear of the orificed. baiile.

An object of the present invention is to provide a method and apparatus of the character described adapted forfaithfully responding over a sufllciently level response over a wide band' width. Another feature of the present invention pro vides an attachmentfor use in combination with the two diaphragm loud speaker, for attaching the loud speaker to a conventional horn, for example, to a theatre horn or an auditorium horn, for replacing the single diaphragm loud speaker units of the prior art, or for replacing the two loud speakers of the prior art sound systems with a two diaphragm single loud speaker adapted 'for'more faithful reproduction of sound over a wider band of audiofrequencieafor eiiectively improving the articulation, the intelligibility and the illusion of reality desired .by theatre managers and sound engineers. This feature of the invention is also adapted for use in radio-audio, and in radio-audlo-television receiving systems by employing tubular acoustical conduction within the apparatus cabinet behind the baflie acoustically associated with the direct acting type diaphragm, in a modification ofthe apparatus described and claimed in one or the other 0! my reissue U. S. patent, Re. 20,395 hereinbefore identified. A cooperative oriiiced baflie modification of the apparatus described in this reissue patent is shown and described herein with reference to the accompanying drawing.

The coupling-dividing, or compensating coils, transformers and circuit networks herein shown 1 and described are modifications of the apparatus described in eithermy U. S. Patent No. 2,189,161

issued Feb. 6, 1940; or in my copending application for Letters Patent in the U. S. Serial No.

' 317,266 filed Feb. 5, 1940.

. Other features of my invention too numerous taken together or separately. For the sake of explaining the principles of the invention, I will now describe illustrative embodiments thereof. The drawing is for illustrative purposes only and is not drawn to scale. The details of mechanical construction being left to the skill oi experienced workmen employing the apparatus herein described and claimed.

In the drawing: a

Fig. 1 represents a modification of electroacoustical and electro-dynamic apparatus embodying the invention.

Fig. 2 represents an attachment for connecting the device shown in Fig. 1 with an external horn, or with a tubular resonant air-column load.

Fig. 3 represents a coupling and dividing network for connecting the signal current coils of the device shown in Fig. l to a circuit network.

Referring to the drawing:

In Figures 1 to 3: electro-acoustical devices of the electro-dynamic type may be electro-magnetically energized, or they may be of the permanent magnet type, according to the particular conditions encountered.

For example, in a radio-audio receiving system operating from a power supply line, the electron"; gnetic field supply by means of a field coil may be satisfactorily employed, but in auto-radioaudio systems and farm battery radio-audio systems, and in address-auditorium and theatre rid systems where the loud speaker is often at a distance from the audio frequency 'mplifler from the power source, permanent et electro-dynamic loud speakers are preferr used.

modifications illustrated in the accompe yang drawing show the electro-magnetically enei Lzed system, but it is understood that in order to get usefulness from'this invention either method of energizing the magnet of the electro-dynam'ic actuating means may be employed within the scope of the claims.

Permanent magnet devices are also employed with electro-dynamic microphones. Therefore when the devices of the present invention are used as microphones or in systems where the electro-magnetic field supply is not readily available, the devices of this invention may be of the permanent magnet electro-dynamic type.

The form of the magnet illustrated readily adapts the magnet for either a permanent magnet or an electro-magnet. When used as an electromagnet an H form as shown may be used, or any other suitable form. When used as a permanent magnet an H form may be used or any other form may be used. When separated the magnet may be U shaped, or round, or any other practical shape.

The diaphragms may be arranged whereby one diaphragm responds more effectively at one end of the audio range of frequencies, while the other diaphragm deals more effectively with the other end of the audio band of frequencies. 01' any desirable relative response arrangement may be employed for obtaining desired results.

Parallel magnetic circuits are employed for more flexibility in obtaining compensation and tone control than may be had from a series mag netic circuit arrangement, where any compensation applied to one magnetic pole and air-gap, or to the associated signal current coil in the said air-gap will also tend to modify currents passing in the series magnetic circuit through the other pole end and magnetic air-gap and through the second signal current coil therein. In the parallel magnetic circuit system of this invention improved electro-acoustical and electro-dynamic features are provided.

Cooperative orificed baffle means is another feature of the invention in the acoustical compensation portion thereof for cooperating with the direct acting type diaphragm of the invention.

Sound waves continue to spread in free air, with only a very small loss due to the absorption of the sound by the air itself. When however, the waves reach any solid body, they are in general partly transmitted, partly reflected, and partly absorbed. Many solids as is well known transmit or conduct sound very well indeed. The transmission or phragm action, if the solid is in the form of a panel, as an oriflced home, by sound-board resonance action when the orificed battle is cooperatively acoustically coupled with a loud speaker as herein shown in the accompanying drawing and described in the specification, which is in accordance with my U. S. Reissue Patent 20,395 hereinbefore identified.

When a direct acting type diaphragm produces the lower tones, the slow air oscillations corresponding to these tone ranges on either side of the diaphragm have, as is known, the tendency to equalize around the rim or periphery of the diaphragm.

In order to obviate this, a baffle is usually arranged to extend from adjacent the periphery of the diaphragm. The orificed baffle of the present invention not only prevents the direct equali :ation of the air vibrations corresponding to the lower tones, but intensifies them by resonance.

Baffle, or sound-board resonance added to resultant tones tends to effect the lower tones more than the higher tones. The lower tone ranges are usually not brought out with proper effective proportionate relationship with other higher tones by the diaphragm alone.

The acoustical coupling between the peripherial portion of the loud speaker and the associated baffle are very important features determining the quality of tones emanating from apparatus of the class herein described. The tubular resonant air column conduction action of the present invention in cooperation with the orificed bafiie of the device tends to bring out a wider band of audio frequencies having improved resultant tones.

In Fig. l, electro-dynamic electro-acoustical device I may be a loud speaker i, a microphone I, or both a loud speaker and a microphone in a single unit i, wherein one diaphragm may be connected for use as a microphone and the other diaphragm connected for use as a loud speaker.

Element 2 is a mounting for the unit having an annular peripherial supporting portion 3 or IA for the direct acting type diaphragm I. The flanged periphery 4 of the substantially conical diaphragm I is supported by the mounting portion IIA of the mounting 2 and the ring shaped or annular baille portion 31 of mounting 2. Mounting portions 3 and 3A show two different arrangements. Arrangement 3A is a modification of the apparatus described and claimed in Re. Patent No.

conduction may be partly due to a resonant dia- Mounting portion 3 is a modification showing one of the soundboard and loud speaker arrangements in combination with a ring shaped auxiliary baifle member 31, described and claimed in my U. S. Reissue Patent No. 20,467.

Auxiliary baiile member 11 interposed between the flanged periphery l of diaphragm I and the rear surface of orificed battle ll spaces the periphery 4 ofdiaphragm I rearwardly from baths 3!. Auxiliary baiiie member I! may be composed of any suitable material adapted for cooperatively and freely conducting sympathetic vibrations between the mounting portion l-IA and the flanged periphery I of diaphragm I and the rear surface of the oriflce'd bame III whereby sound vibrations are caused to be modified or modulated by means of cooperative acoustical conduction resonance action between the said associated elements I3A, I and I! in combination with sound board resonance action of the orinced baiile 38.

Screws or bolts 39 secure device I on the rear side of the baffle 30. Baiile 38 forms a baflle "support" for the electro-acoustical electro-dynamic device I. Fabric 40, which may be for ornamental purposes, or for acoustically damping the resonant action of baihe 38, or which may be both useful and ornamental, is applied to the front surface of ballie ll and across the oriflced portion thereof.

Asuitable gasket ll of cardboard, flbreboard, rubber, felt, or other suitable material is applied between the front end of the horn l and the annular portion 43 of baiiie ll, the bame portion 48 provides the oriflced portion 44 in baflle ll substantially concentric with diaphragm 6 and a larger oriflced portion ll providing free Dassale for sound waves between the front surface 40 of diaphragm I! and the outer surface 41 of the horn 35 to the atmosphere, or from the atmosphere to the fluid area between the inner surface 48 of diaphragm 5 and the outer surface 41 of horn 35.

Grill elements 42 may be provided across the oriflced portion 44 of balile 38 for ornamental purposes, for protective purposes, or for providing damping compensation forthe resonant air column 36 within horn 3 5.

Baiile support" 38 may be composed of metal, wood, cardboard, flbreboard, ply-board, or other suitable material. The baiile I! may be an element of device I forming a support for device I, v

or baflie 38 may be mounted in a cabinet, or baffle 30 may be mounted on a radio-audio receiver chassis, or in any other suitable arrangement within the spirit of the invention, subject to my U. S; Reissue Patent 20,395 hereinbefore identifled. I

Mount ng 2 of device I may be U shaped, or the mounting 2 may be stamped out of any suitable sheet material, which is lighter, cheaper, and simpler for construction purposes than prior art solid or rigid cast mountings.

Direct acting type diaphragm I carries a signal current coil 6 projected inthe magnetic aira gap 1 of the electro-dynamic actuating unit 8.

Electro-dynamic actuating unit 9 has parallel actuating units 8 and i0, providing parallel magnetic circuits divided at the cross-sectional line H shown in Fig. 1. Magnet portion B has an outer apertured pole plate l1 forming a support I2 for attaching the unit 9 to the mounting portion 2 of the mounting 2.

The other magnet portion II has an apertured outer pole plate I! at the rear of device I. Numeral l4 indicates. a common magnet portion having an aperture l5 therein. Magnet portion 8 includes an inner pole piece I. Magnet portion l0 includes an inner pole piece ll. Inner pole portions or pieces l6 and II are hollow and open at both ends. The outer end of pole piece it projects into aperture I in outer pole plate I! forming the annular air-gap 1. The outer end of inner pole piece 11 projects into aperture II in the outer pole plate ll forming the annular air-gap I8.

A relatively solid small type diaphragm I! having a dome shape and a peripherial supporting portion and carrying a signal current coil 20' projected in themagnetic air-gap II, is mounted between rings of suitable material il-fl, such as cardboard, flbre, leather etc., and attached to the outer side of the pole plate II, the diaphragm i. being in acoustic relationship with the air col umnli within the inner pole portions lt-ll and common magnet portion II.

The inner ends of pole pieces II and I1 are butted against the commonportion ll of the magnet l on opp site sides of aperture a single tubular air column ll is formed thereby open at both ends.

The magnet portions ll-HA and ll-ilB may be cast of suitable material in one piece or block, or the magnet portions l4-HA and I'4 B may be separately stamped out of suitable sheet metal in U shape. The two separate portions may then be placed back to back as shown by numerals I and Ill and fastened securely to gether forming a single unit 9. Various means" are suitable for fastening portions 8 and III together when this construction is employed, such as welding, riveting, bolting. screwing, etc. The inner pole portions IO and I1 may be a single element li.l| inserted through aperture I! in common magnet portion I, and securely fastened to portion N with the outer ends thereof projecting into apertures I and II in outer pole plates l2 and II respectively forming the magnetic airgaps' I and ll therein, in which case air column ii is separated from aperture is in the common magnet portion I through which the inner pole portion will project, as shown by the dashed lines in'Fig. 1 across portion H. The drawing shows the magnet portions ll-HA and HB cast in block. The particular details of mechanical construction will vary according to the particular conditions encountered depending obviously greatly upon the particular use to which the device will be put, and are therefor leftto the skill of the experienced workmen employing this method and apparatus within the-spirit of the invention and the scope of the claims, various modiflcations being possible, according as to whether the device is employed as a loud speaker, or as a microphone, or as both a loud speaker ll so that and as a microphone wherein one diaphragm is constructed and arranged for a microphone and the other diaphragm for a loud speaker.

A flexible member 23 is attached to the cylindrical sleeve 24 carrying the signal current coil I on diaphragm U, and is also attached to mounting portion 2 by screws 25. Washers 26 space flexible member 23 from mounting portion 2' for locating the signal current coil 6 in the proper position in magnetic air-gap 1 flexibly movable for best effective desired results.

The peripheral supporting portion of diaphragm I! may be flat 'or corrugated according to the amount of flexibility desired. A member 21 secures the periphery of diaphragm l8 associated with rings Ii and 22 to the pole plate It so that a small resonance space or chamber 28 is formed between diaphragm I9 and pole plate 13; another small resonance space or chamber 29 being formed between the other surface of diaphragm I. and the member 21.

Diaphragm II is attached to pole plate I! so as to vibrate in accordance with electro-acoustical vibrations or currents associated therewith. The chambers 2| and 29 tend to provide compensation for controlling the mechanical motion of the diaphragm ll utilizing the mass, elasticity and viscosity-of the air to efllciently damp the mechanical motion of the diaphragm Is.

An aperture or apertures I0 through pole plate II provides air pressure or resonance release for modifying the damping effect of chamber 2! upon diaphragm II. An aperture or apertures II profor maximum efficiency in accordance with a desirable characteristic curve according to a wide audio band width having a sharp cut-oil and at the same time preserving a sufiiciently level response over a wide band width.

A casing 32 may be employed in combination with device I and diaphragm [9 as part of actuating unit 9, providing an additional resonance chamber 33 forming an acoustical load on diaphragm i9 through the aperture or apertures 3! in member 21.

The insert 34 located in the tubular air column i within the inner pole portion ii is secured concentrically therein in spaced relation to the walls of the air column i5 by means of suitable fins or guides, providing a load on the adjacent surface of diaphragm IS. The insert 34 is of such shape as to provide an air passage through the chamber i5 increasing in cross-section gradually from adjacent diaphragm H. The insert may be solid as shown, or the insert 34 may be perforated by one or more tubular chambers, 15, as indicated by the dashed lines therethrough longitudinally therewith, the insert 34 may be in other forms,

and when the device i, or the portion in of cle- 1 vice I is employed as a microphone the insert may be omitted.

A horn 35 having a resonant air column 35 therein may be attached to the forward end of inner pole portion it as shown. The forward end of pole portion l 6 and walls of tubular air column i5 therein are recessed for having the horn 35 secured thereto so as to form an extension of the air column I5 through the open portion of direct acting type diaphragm 5 to a region in front of diaphragm 5 substantially concentric with the periphery thereof and substantially concentric with the orificed portion 45 of the bailie 33.

Diaphragm 5 is in the form substantially of a truncated cone having a flanged periphery 4, carrying a signal current coil 5 and having an open portion adjacent the signal current coil 5 through which horn 35 is projected.

When device i is employed as a two diaphragm loud speaker sound waves emanating from the diaphragm IE will pass through air column I5 to air column 36 within horn 35 and through horn 35 to the region directly in front of diaphragm 5, in substantially the same general direction as sound Waves propagated from the front surface of diaphragm 5 through orifice 45 in baffie 38 to the outer atmosphere and substantially concentric therewith.

Plural field coil windings 40 are applied to pole portions i 5 and i! for energizing the actuating unit 9. A stationary electro-dynamic compensating coil or biasing coil 49 is applied to pole portion l8 and connected in series with signal current coil 5 carried by diaphragm 5. Another stationary electro-dynamic compensating or biasing coil 50 is applied to pole portion i1 and connected in series withthe signal current coil 20 carried by diaphragm ii.

The compensating or biasing coils 49 and 50 are features of the present invention carrying forward the basic idea disclosed in my U. S. Patent No. 2,189,161 issued Feb. 6, 1940.

In the present invention the coils and or a coil 49 or a coil 50 provides compensation tending to bring the two diaphragms into proper reschance for the most efficient operation in accordance with a desirable characteristic curve according to a wide audio band width having a sharp cut-off and at the same time preserving a sufliciently level response over a wide band width.

The compensating or biasing coils may be employed with either permanent magnet electrodynamic devices or with electromagnetic electrodynamic devices employing two or more diaphragms in a network system. Only a few turns are necessary for biasing coils 49 and 50. The coils 49 and 50 may be connected or arranged in various ways for providing compensation within the spirit of the invention and the scope of the claims. My Patent No. 2,189,161 covers the use of a stationary electro-dynamic coil in other single diaphragm arrangements.

Circuit leads 5| and 5Z-may be connected to any suitable audio frequency circuit system, in either the input portion of the circuit or the output portion of the circuit within the spirit of the invention without departing from the scope of the claims.

Circuit lead 5i is connected with coils 5 and 49; circuit lead 52 is connected with coils 20 and 50. Leads 48A are the field coil leads for field coil 48 applied to the actuating unit 9.

In Fig. 2, another modification of member 21 is shown, indicated by numeral 21A in combination with an attachment 53, for connecting the .portion 10 of device i and diaphragm IS with an external horn or tubular resonant air column load, such as a horn'of the type employed in auditoriums, theatres and other places of entertainment, formed to project sound waves to the atmosphere at an angle of substantially to the intake throat portion thereof.

The attachment 53 makes the device I suitable for a wider range of usefulness in the entertainment field. For example, a bass horn may be attached to device I by means of attachment 53 for bringing out the lower tones. The opposite surface of diaphragm I!) being operatively connected with the horn 35 arranged for higher frequencies, while the direct acting type diaphragm 5 may be arranged to function over the intermediate band of audio frequencies or any suitable portion of the audio frequency band, as between 50 cycles and 7,500 cycles, or between 300 cycles and 10,000 cycles, or diaphragm 5 may be arranged to bring out the lower frequencies and diaphragm 19 arranged to bring out the higher frequencies.

Instead of device 53 connecting device i with an external horn, the device I may be connected with a tubular air column within an apparatus cabinet and device i located in an apparatus cabinet, such as in combination with a radio-audio receiver, or with a common radio receiver and amplifier for picture and sound, in a modification of the apparatus described and claimed in my Reissue Patent Number 20,395 hereinbefore identified. The present invention carries forward the basic idea of the invention therein disclosed.

The portion 213 of element zlA'is modified so that the aperture or apertures IIA provide passage means from diaphragm I! to the throat IIB of the attachment 53 having impedance suiilcient for providing a load on the adjacent surface of diaphragm l9. Apertures 54 are provided in device 53 for the passage of screws or bolts for attaching device 53 to actuating unit 9, or to portion i3 thereof.

In Fig. 3, a oupling-compensating-dividing network system is shown, indicated by numeral 54, which is a modification of the inductanceimpedance combinations and circuit networks described and claimed in my U. S. Patent No. 2,189,161, and in my copending application for U. S: Letters Patent Serial No. 317,266 hereinbefore identified, carrying forward the basic idea therein disclosed, providing a dividing network system .54 employing two transformers and inductance-impedance elements, in an audio frequency circuit system employing two diaphragms each diaphragm carrying a signal current coil connected to the network 54 by means of circuit leads and 52, shown in Fig. 1.

Transformer T is described and claimed in U. S. Patent No. 2,189,161, having a winding divided at an intermediate tapping point 55 and an impedance comprising a transformer winding, in transformer T2, a resistance unit 59 and a condenser 6i and a resistance 69 connected in parallel with the outside tapping points of the transformer winding 55.

Resistance units 59 and 60 are for individually I adjusting or regulating the volume or tone associated with each coupled diaphragm, as 5 and I9 shown in Fig. 1. Resistance units 59 and 69 may be variable, or they may be of the type havin a sliding contact adapted for being permanently secured in position when the proper setting is determined, or they may be fixed resistance units of the value found to effect the best cooperative results. Condenser 6| provides a capacitive impedance adapted for modifying the tones of current frequencies passing through transformer T2 and circuit 52 to diaphragmi 9 in combination with winding 56 and resistance 59 forming an impedance in series with the transformer winding connected to point 54 of the dividing network system. Transformer windings 51 and'59 provide coupling network circuits for connecting the dividing network 54 with circuit leads 5| and 52 of device 1 shown in Fig. 1.

The device I in Fig. 1 is not shown connected to the coupling-dividing-compensating network 54 of Fig. 3 because I desire to bring out that this application is a continuation in part of my copending application serial No. 317,266, and that the several coupling networks described and claimed therein provide improved coupling arrangements and circuit networks for connecting circuit leads 5! and 52 of the device I with the dividing circuit network leads and windings 51 and 59, of the network system 5.4, or of any other suitable network in an audio frequency circuitsystem.

We meet with resonance in the diaphragm of a microphone or of a loud speaker, in the human voice, in drums, disk recorders, and other places. Sounding bodies usually have several natural resonances, strings vibrate as a whole and also in parts, and the same is true of air columns, diaphragms and bailles or sound-boards. These various resonances are set up concidently and are responsibl for the components or overtones elicited from the device or instrument. Without resonance there is no tone quality.' A sound reproducing device designed to avoid resonance will eliminate the necessary components or overtones necessary for bringing out depth, timbre and brilliant tone quality.

In the case of the stringed instruments, in cluding the piano, instruments of the violin family, plucked string instruments etc., the vi-' brations of the strings are communicated to the body or sounding board and the tone quality is determined by the resonance of the sounding board and the air-column of the resonance chamber of the instrument acting to blend overtones with the fundamental tones produced by the instrument.

This is the basic principle and the basic. idea upon which my methods and apparatus are based.

Cabinet cavity resonance" is another and different kind of resonance, (see resonance defined in Websters International Dictionary.)

My methods and apparatus employ resonant diaphragm and acoustical conduction resonance" action. My methods and apparatus avoid cavity resonance" in the apparatus cabinet, that causes reverberation distortion.

It is inherent in apparatus of the character described that some vibrations will be impressed upon the baflie 38 by the elements of sound reproducing device'l or 1|. bailie member 3'1 tends to make these vibrations sympathetic." Sympathetic vibrations have the same period of vibration as the body they cause to vibrate, causing an increase in intensity and amplitude of said vibrations, by resonant diaphragm, or conduction resonance.

Numerous ideas have been carried out in this invention, with recognition on my part that one or more novel elements, arrangements or combinations can be employed separately, or the various elements, arrangements, or' combinations may be employed collectively. I want it understood that I do not limit my invention. I realize that other modifications are possible and it is my Be. 20,395 issued June 8,1937; 2,189,161 issued Feb. 6, 1940; or application, Serial No. 317,266 filed Feb. 5, 1940.

I claim:

1. In combination in an electro-dynamic electro-acoustical device forming a loud speaker, two diaphragms each carrying a signal current coil mounted on a cylindrical sleeve attached thereto, one diaphragm having a relatively stiff curved central portion and a flanged periphery permitting the stiff central portion of the diaphragm to move relatively to the fixed outer periphery thereof, the other diaphragm having the form substantially of a truncated cone having an unobstructed open-center portion coinciding with the sleeve and coil carriedthereby, and having a flanged periphery, and two electro-dynamic field magnet units including a pair of inner pole portions one in front of the other, a pair ofvv netic air-gaps one in front of the other, and

apertured magnet yoke portions in adjacent relationship supporting the butt ends of the inner pole portions and connecting the two field magnet units in adjacent concentric systems, the inner magnet poles being hollow and open at both ends forming a single open ended air column extending through the apertured yoke portions of the magnet system, the two air-gaps and the two diaphragms being located adjacent opposite ends of the inner magnet poles, separate mountings for the two diaphragms attached to the magnet system supporting the peripheries thereof in a fixed position, a flexible member associated with the conical diaphragm and its Auxiliary ring-shaped mounting flexibly suspending the sleeve and coil movable in one magnetic air-gap, the signal current coil carried by the smaller diaphragm being flexibly suspended movable in the other airgap wherein the contour of the smaller diaphragm and the adjacent portions oi the magnet poles coincide, the arrangement forming a chamber having small volume between the smaller diaphragm and the magnet poles, and an oriilced baffle member applied to the opposite side of the smaller diaphragm, the orificed portion of the baffle forming passage for sound waves from one side or the battle member to the fluid area on the opposite side of the baiile member in acoustical relationship with the smaller diaphragm, and a horn attachment applied to the device on the outer side of the orificed baiile member having communication through the orificed portion of the baffle with the smaller diaphragm, the arrangement forming a chamber having small volume between the adjacent surface of the baiiie member and the smaller diaphragm, the mass, elasticity and viscosity of the air in the said two small chambers tending to cooperate in emciently modifying the mechanical movement of the smaller diaphragm.

2. An electro-dynamic electro-acoustical device forming a loud speaker including a combination of elements substantially in accordance with claim 1, wherein an oriflced bai'iie member is applied in the smaller diaphram having a surface contour adjacent the smaller diaphragm substantially coinciding with the contour of the smaller diaphragm arranged and iorming a chamber having small volume between the said adjacent surfaces oi the smaller diaphragm and bame member, and a horn attachment applied to the outer side ofthe oriiiced baiiie member, the horn attachment interior having communication with the outer side of the baiiie member forming at least one passage chamber having relatively small volume between the bai'iie member and the interior wall surface of the horn attachment having communication with the intake throat portion or the horn attachment and also having communication with the first said cham' bar and the smaller'diaphragm through the orinced portion of the baiiie member.

RAYMOND E. BOWLEY. 

